The present invention relates to a device and method for support of a coolant feed line for superconducting machines. In particular the present invention relates to a device for supporting a long coolant feed line. Such a device in accordance with the preamble is known from DE 103 58 341 A1.
Superconducting machines, such as synchronous motors or generators with a superconducting rotor winding for example, have been able to be used commercially since the discovery of high-temperature superconductivity in materials such as YBCO and BiSCO, which exhibit their superconducting effect at an operating temperature of 77K. Such a superconducting machine is known for example from DE 103 58 341 A1.
FIG. 1 shows a possible layout of such a superconducting machine 100 with a cooling unit 200 connected thereto. So that the superconducting machine 100 operates as such, the superconducting winding present in the machine must be cooled down beforehand to its working temperature of 77 K or lower. For this purpose a suitable coolant is introduced into an internal space of the rotor 110 of the machine 100 embodied as a shaft. This internal space of the rotor is connected for this purpose to the cooling unit 200 via corresponding means 300. The cooling unit 200 cannot be connected directly to the machine 100. Instead suitable sealing of the internal rotor space from its surroundings must be ensured, so that no heat leakage or any associated adverse influence on the superconducting effect occurs. In addition a suitable seal must also be provided between the rotor shaft 110 rotating around its axis and the stationary cooling device 200. This is achieved by an appropriately embodied hollow shaft 320. To avoid a leakage of heat this hollow shaft 320 must however be embodied of sufficient length for a given cross-section. Located within the hollow shaft 320 is a coolant feed line 310, which is permanently connected to the cooling unit 200 and feeds the coolant from the cooling unit 200 into the hollow space of the rotor 110. The hollow shaft 320 is permanently connected in this case on one side 320″ to the rotating rotor shaft 110. On the other side 320′ a suitable sealing device is provided between the rotating hollow shaft 320 and the fixed coolant feed line 310. What are referred to as heating tubes 311 can be provided for example within the coolant feed line 310, which take over the actual transport of the coolant.
Within the hollow shaft 320 the coolant feed line 310 is supported on one side 320′ by the sealing device and thus spatially fixed. On the other side, the machine side 320″, the coolant feed line 310 is fixed spatially via a magnetic support 400. The magnetic support 400 is based on a superconducting and/or permanent-magnet support. Superconducting supports are very cost-intensive, since superconducting materials are expensive and complex to manufacture. A further disadvantage is the necessary cooling to below the transition temperature of the superconducting material, in order to ensure the operability of the superconducting support. This makes the support susceptible to faults and limits its spatial arrangement in the machine 100. Permanent magnet supports are heavy and are likewise cost-intensive. The weight of the permanent magnets loads the end of the coolant feed line 310 which lies on the machine side 320″, and thus acts against the stabilization of the end. To counter the destabilization the coolant feed line 310 and the hollow shaft 320 must be constructed as massive elements. This increases the cost and leads to a deterioration in the machine characteristics.
A machine 100 without a magnetic support 400 on the machine side 320″ leads to a freely-movable coolant feed line 310 on the machine side 320″ without spatial fixing. The fact that the coolant feed line 310 is only fixed on one side, but is freely movable at the other end of the hollow shaft, means that the coolant feed line 310 can be excited into oscillations. It is precisely with the lengths of the hollow shaft 320 required in superconducting machines that the resonant frequency of the coolant feed line 310 caused by said oscillations can lie in the working range of the rotational frequencies of the machine 100. Accordingly this frequency, as the operating frequency of the machine. must be explicitly excluded. Thus attempts can actually be made, through corresponding constructional measures on the coolant feed line 310, to keep the resonant frequency outside the rotational frequency range of the rotor shaft 110 and thereby outside the permitted working range of the machine 100. This is becoming increasingly more difficult however as a result of the demand for ever smaller sizes of superconducting machine and thus ever thinner hollow shafts with the simultaneous desire for higher speeds.